When I began Pacific Northwest ocean diving I was fascinated by hooded puncturella (Cranopsis cucullata) limpet shells. These interesting shells usually have 16 strong radial ribs that extend down to the margin. The margin (basal edge) has a scalloped pattern because of the pronounced ribs. There is also a small elongated slit near the top (apex) of the shell. The hooded puncturella can grow to 1.7 inches (4.2 cm) across, with a range from central Alaska to northern Mexico.